Volume pot crackle only when there is a signal

[Zoldar71]

Hi, I have a Princeton Reverb clone from Tube Amp Doctor with a crackle when turning the volume pot (from around 2-4). But only when there is signal. When there is no signal the pot is dead quit. I cleaned it two times with contact cleaner, but the crackle remains.
I have fixed quite a few crackling pots before, but the difference is that they also seamed to crackled when there was no signal.

So my question to the experts. Replace the pot or can it be something else in the circuit?

Help is much appreciated.

[Chuck H]

Have you tried another tube in the V1 socket?

[Zoldar71]

Oh I can do that. Thanks for the suggestion. I will try and report back.

[g1]

Sometimes it's normal. You are not going to be making adjustments while playing a song.

[Zoldar71]

Chuck H: Thank you for the tip. Swapping V1 with another 12AX7 solved the issue or at least drastically reduced it. But what is even better it also solved another much bigger problem. When playing on the thick E there was a rattle like sound that I couldn't find the source off. I thought it was something mechanical rattling, because it sounded like that. By swapping the tubes also that is gone.

To help me understand, is the tube bad? And should I replace it, or can it function still as V3 or V4?

[xtian]

Yes, a tube that is noisy in V1 can sometimes be fine later in the circuit.

[Chuck H]

Modern tubes can sometimes do funny things WRT DC interactions. Spacing specs, materials purity, etc. Who knows. But it's not like it once was. I've seen all manor of odd things happen with modren production tubes.

The low E anomaly is actually a typical problem with hot strat pickups. It's probably that the gain of the substitute tube is a little bit lower than the one you had in there. Physically lowering the bass end of your offending pickups would also help (tip from uncle Chuck )

It doesn't seem that the tube was actually the problem but the lower GM of the one you substituted put things back in useful order. I suspect there may be a shared ground scenario that is less than ideal in the preamp stages of your amp.

[Zoldar71]

Thank you guys, then I leave it like it is now. On the possible ground scenario issue, I followed attached layout to the letter. I will double check all connections and solder joints. But looking at this layout what do you think would be less than optimal ground wise?

[Chuck H]

Are you using a shielded lead from the center lug of the volume control to the 12ax7 grid?

[Zoldar71]

Hi Chuck H. No I'm not. Maybe I will implement it. Is it also a good idea to replace the red wire coming from the input jacks with a shielded wire?

[Chuck H]

If the amp is performing stable without shielded cable then there's no need to add it. I asked because sometimes long shields can do funny things depending on how they're connected. So I was wondering if a shield could be causing your problem.

[drewl]

I had a weird problem like that with an SVT2
Master pot would crackle when turning standby on, but only for about 20 seconds, as soon as voltage stabilized it was fine.

[Zoldar71]

Thanks everybody for the great help and insights. Learned a lot. This weekend I will be working on my amp. Checking all the ground points. But I think the tube swap was the golden tip!
Now I will read up on the thick E causing rattling sounds Chuck mentioned. Very interesting.